The present invention relates to a method for multiplexed data transmission from such hazardous environments as fuel loading stations to a "safe area" computer, as well as means including hardware and software for practicing the method of the invention,
Numerous problems have arisen in the transmission of data between a plurality of non-stationary objects in a hazardous environment to a safe area computer, As an example of a system in which such problems can arise, one can postulate a fuel loading station wherein trucks or other vehicles regularly come into physical contact with a plurality of fuel dispensers, and a master computer in a safe area remote from the hazardous environment of the fuel dispensers performs such functions as verifying from coded digital data that a particular vehicle in contact with one of the plurality of fuel loading dispensers is authorized to receive fuel, sending control signals to the particular dispenser to allow fuel to be pumped into the vehicle after verifying that the vehicle is an authorized one, and storing in memory such information as the type and amount of fuel and the time at which such fuel was pumped into the authorized vehicle.
One way in which the transmission of digital data and control information between non-stationary objects in a hazardous environment and a safe area computer has been accomplished in the past was a method comprising the coupling of an amplitude modulated signal between the respective non-stationary objects and the safe area computer via transformer action. However, a system using such a method has a high susceptibility to electrical interference and also suffers from the problem of degradation of the transmitted signal when long cable lengths are involved. These two factors of course negatively affect the integrity of any digital data received in the system. Also, such systems have the additional problem of extremely complex receiver circuits including the need for automatic gain control (AGC) circuit elements.